The present invention relates to pressure responsive electrical switch assemblies, in particular to pressure switch assemblies of the type wherein it is desired to have a pair of electrical contacts that, upon increasing fluid pressure to a sensing cavity, close at a specified pressure, remain closed upon increasing pressure, and reopen at a predetermined upper limit pressure. Upon decreasing pressure from the upper limit, the contacts reclose at a specified differential below the upper limit pressure, remain closed for a predetermined pressure differential, and then again reopen at a point below the initial closing pressure on increasing pressure. Such pressure switch action is sometimes referred to as "make-before-break" action. This type of pressure switch operating characteristic has found particular application in automotive air conditioning systems for controlling the cycling of the compressor clutch in response to sensed variations in the pressure of the refrigerant entering the expansion valve.
In providing pressure switches capable of responding as described above to increasing and decreasing pressure over a broad range of pressures, it has been desirable to provide a snap-action to the switch to prevent arcing and prolong the life of the electrical contacts. However, in order to provide snap-action to the making and the breaking of the switch, it has proved difficult to provide a make-before-break operation on increasing pressure because continued travel of the pressure responsive means in one direction upon increasing pressure after the making of the contacts has been found to be mechanically complicated. Known devices for achieving this type of operation have employed beam type springs, wherein the pivot point of the spring is changed by contacting a stationary support after a predetermined amount of movement. Upon continued movement flexure of the spring is reversed about the stationary pivot, thereafter increasing the stiffness of the spring and decreasing the sensitivity of the switch.
It has thus been desired to provide a pressure switch capable of make-before-break operation on increasing pressure and similar make-before-break on decreasing pressure, which has a construction that is simple and relatively low in cost to fabricate and assemble in mass production, and which provides reliable operation.